Optical switch array using rolling shutter optical switch elements

ABSTRACT

An optical switch device includes a rolling shutter or membrane attached at one of its edges to a substrate near an optical port in the substrate. The rolling shutter can assume one of two states. In a first closed state, the membrane is uncoiled onto the substrate over the port such that light directed at the port impinges on the shutter. In a second open state, the membrane is rolled up away from the port such that light directed at the port impinges on the port. In one embodiment, a mirror is formed on the membrane such that when the membrane is in the closed state over the substrate, light directed at the port is reflected by the mirror. In one configuration, the optical port includes a hole or aperture such light passed through the port without interference. The device can include a latch electrode the far end of the membrane such that when it is rolled out, it can be held in position by a latching voltage applied across the latch electrode and the substrate. Slits can be formed in the membrane to keep the mirror flat by relieving strain in the membrane and to allow gases in proximity to the device to pass through the membrane as it is activated. The shutter can include dimples to minimize the area of contact between the membrane and the substrate to reduce the probability of the two sticking together. The attachment edge of the membrane can be made shorter than its width to reduce distortions in the membrane to keep the mirror flat. A raised annular rim can be provided around the port such that when the shutter is held down over the port it is pulled taut and flat over the rim. This feature is also used to maintain flatness in the mirror. The switch device can be used as part of an array of optical switches.

RELATED APPLICATIONS

[0001] This application is based on U.S. provisional patent applicationSer. No. 60/187,226, filed on Mar. 3, 2000; U.S. provisional patentapplication Ser. No. 60/188,119, filed on Mar. 9, 2000; and U.S.provisional patent application Ser. No. 60/220,355, filed on Jul. 24,2000.

FIELD OF THE INVENTION

[0002] The present invention relates to an improved optical switchdevice with a rolling shutter in which, when the shutter is in an openposition, light passes impinges on a substrate of the device, and whenthe shutter is in a closed position, light is reflected back by theshutter.

BACKGROUND OF THE INVENTION

[0003] Optical switch devices have been developed in which a movableshutter is mounted on a smooth flat substrate. The shutter is positionedsuch that light is directed toward the substrate in proximity to theshutter. The shutter is made of a thin material which has stressesintroduced such that the shutter is normally in a coiled configuration.As a result, light directed onto the substrate is able to pass throughthe substrate without obstruction from the shutter. When a voltage isapplied across the substrate and the shutter, the resulting electricfield causes the shutter to uncoil into a flat position over the surfaceof the substrate. Light directed onto the substrate therefore impingeson the uncoiled shutter. Such a device can be implemented in a varietyof optical switching applications.

[0004] For example, U.S. Pat. No. 5,233,459, issued on Aug. 3, 1993,entitled “Electric Display Device,” describes an optical switch devicewith a movable shutter. The shutter is formed on a glass substrate suchthat when the shutter is coiled up, light can pass freely through thedevice. When the shutter is uncoiled, it is held in a relatively flatstate over the substrate by the electric field applied between theshutter and the substrate. In this state, light impinges on the shutter.

[0005] Such devices are prone to several drawbacks. For example, theshutter can have a tendency to stick to the substrate. When the electricfield is removed or reduced, the sticking interferes with the ability ofthe shutter to recoil. This can cause substantial delays in devices andprocesses which utilize the device, or can result in complete failure ofthe devices and processes. Also, the gaseous atmosphere in which thedevice operates can slow the opening and closing of the shutter, alsoresulting in delayed processing. Also, the shutter can tend to distortwhen it is uncoiled.

SUMMARY OF THE INVENTION

[0006] The present invention is directed to an improved optical switchdevice or element, an array of optical switch devices or elements and anoptical switching method. The optical switch device of the inventionincludes a substrate and a flexible membrane or shutter attached at oneof its ends to a surface of the substrate. The substrate includes anoptical port portion on which light can be made to impinge. The flexiblemembrane is attached to the substrate in proximity to the optical portportion of the substrate. The flexible membrane is configured such thatit is controllable between a first or closed state and a second or openstate. In the closed state, the membrane is disposed onto the substrateover the optical port portion such that when light is directed towardthe optical port portion of the substrate, the light impinges on theflexible membrane. In the open state, the membrane is disposed away fromthe optical port portion of the substrate such that when light isdirected toward the optical port portion, it impinges on the opticalport portion.

[0007] In one aspect of the invention, a reflective surface or mirror isformed on the flexible membrane. In this configuration, when themembrane is in the closed state, light is reflected by the mirror. Inthe open state, light is allowed to impinge on the optical port portionof the substrate.

[0008] The flexible membrane or shutter is configured such that it isnormally in the open state. When the membrane is fabricated, stressesare introduced into the material such that in a quiescent state, themembrane is rolled up into a coiled configuration. When the membrane isattached to the substrate, and a programming or operating voltage isapplied across the membrane and the substrate, the resulting electricfield causes the membrane to uncoil and lay over the optical portportion of the substrate. Generally, as long as the voltage is applied,the membrane is held in the uncoiled closed state. When the voltage isremoved, the membrane coils back up into the open state.

[0009] In one aspect of the invention, an aperture or hole is formedthrough the substrate at the optical port portion of the substrate. Inthis configuration, when the membrane is in the open position, lightdirected at the optical port portion of the substrate passes through theaperture without obstruction. As in the general configuration set forthabove, when the membrane is in the closed position, the light impingeson the membrane.

[0010] In accordance with another aspect of the invention, the deviceincludes a latching capability which allows the membrane to be held inthe closed, i.e., uncoiled, state without maintaining the operatingvoltage applied across the substrate and the entire membrane. The devicecan be provided with a latch electrode formed on the substrate at theend of the membrane opposite the attachment end when the membrane isuncoiled. When the membrane is uncoiled, the end of the membrane isbrought into close proximity to the latch electrode on the substrate.After the membrane uncoils into the closed position by application ofthe operating voltage, a latching voltage is applied across the latchelectrode and the membrane. The resulting electric field in the air gapbetween the end of the membrane and the substrate holds the membrane inthe uncoiled state. The operating voltage can then be removed. Since anelectric field only exists where there is no contact between themembrane and the substrate, sticking of the membrane to the substrate isreduced or eliminated.

[0011] This latching feature provides several advantages. The latchfeature substantially relieves degraded performance or failure ofdevices caused by sticking of the membrane to the substrate. Without thelatching feature, the operating voltage would be maintained across theentire membrane and the substrate to keep the entire membrane in contactwith the substrate as long as the switch remained in the closed state,in some cases for long periods of time. In such cases, the membraneoften sticks to the substrate, resulting in significant degradation inperformance or complete failure of the device. Because in the presentinvention, the membrane is maintained in the closed position by electricfield in the air gap between the membrane and the substrate only thelatch electrode, the probability of sticking is virtually eliminated.

[0012] In another aspect of the invention, the membrane is provided witha plurality of slits. The slits relieve strain in the membrane andprevent distortion of the membrane when it is pulled down over thesubstrate. The reduced or eliminated distortion allows the reflectivesurface on the membrane to be maintained extremely flat, resulting ingreatly improved performance.

[0013] Another set of slits can be provided to enhance the switchingperformance of the device. Because the device of the invention operatesin a gaseous atmosphere, atmospheric effects can slow the operation ofthe device. This second set of slits is provided to allow the gaseousatmosphere to pass through the membrane as it moves, i.e., as ittransitions between states. Because the slowing effects of theatmosphere are greatly reduced by these gas venting slits, the devicecan change states faster, resulting in improved speed and performance.

[0014] In another aspect of the invention, the membrane is provided witha plurality of dimples, also to reduce sticking of the membrane to thesubstrate when the operating voltage is removed to transition the switchdevice from the closed state to the open state. The dimples provide muchsmaller points of contact between the membrane and the substrate. Holescan be additionally fabricated in the electrodes in the area around thedimples. This has the effect of reducing the electric field in the areaof the dimple. As a result, the probability of the membrane sticking tothe substrate is substantially reduced.

[0015] In another aspect of the invention, a raised annular rim isprovided around the optical port portion of the substrate. When themembrane is uncoiled over the optical port, the area of the membranenear the port contacts the rim. The has the effect of flattening themembrane which improves performance of the device when the reflectivesurface is attached to the top of the membrane.

[0016] In another aspect of the invention, another approach is employedto flatten the membrane and/or mirror. The attachment edge of themembrane, i.e., the edge of the membrane at which the membrane isattached to the substrate, is made shorter than the rest of the width ofthe membrane by forming the membrane with a tapered shape. This has theeffect of reducing distortions in the membrane and thereby allows themembrane to lay flat when it is held in the uncoiled or closed position.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

[0018]FIG. 1A contains an image of a single rolling membrane opticalswitch element with the element in the closed or uncoiled state, inaccordance with one embodiment of the present invention.

[0019]FIG. 1B contains a schematic perspective image of the switchelement of FIG. 1B with the membrane in the open or coiled state.

[0020] FIGS. 2A-2C contain schematic views of a rolling membrane opticalswitch device in accordance with an embodiment of the present invention.

[0021]FIG. 3 contains an image of a rolling membrane optical switchdevice with the membrane in the open or coiled state, in accordance withone embodiment of the present invention.

[0022] FIGS. 4A-4C contain schematic views of a rolling membrane opticalswitch device with a raised annular rim around the optical port, inaccordance with one embodiment of the present invention.

[0023]FIG. 5A contains a schematic view of a rolling membrane opticalswitch device with strain relief slits formed in the flexible membrane,in accordance with one embodiment of the present invention.

[0024]FIG. 5B contains a schematic view of a rolling membrane opticalswitch device with gas venting and strain relief slits formed in theflexible membrane, in accordance with one embodiment of the presentinvention.

[0025]FIG. 5C contains a schematic view of a rolling membrane opticalswitch device with tapered membrane and a shortened membrane attachmentedge, in accordance with one embodiment of the present invention.

[0026] FIGS. 6A-6C contain schematic views of a rolling membrane opticalswitch device with dimples formed in the membrane, in accordance withone embodiment of the present invention.

[0027] FIGS. 7A-7B contain schematic cross-sectional views of therolling membrane optical switch device of FIGS. 6A-6C with dimplesformed in the membrane, in accordance with one embodiment of the presentinvention.

[0028] FIGS. 8A-8C contain schematic views of a rolling membrane opticalswitch device with latch electrode, in accordance with one embodiment ofthe present invention.

[0029]FIG. 9A contains a schematic perspective view of an optical switcharray, in accordance with an embodiment of the present invention.

[0030]FIG. 9B contains a detailed close-up schematic perspective view ofa portion of the optical switch array of FIG. 9A.

[0031]FIG. 10 contains an image of the optical switch array of theinvention illustrating multiple optical switch elements in the open andclosed states.

[0032]FIG. 11 contains a schematic perspective view of an optical switcharray, in accordance with an embodiment of the present invention.

[0033]FIG. 12 contains an image of a switch element mounting structureused in an optical switch array, in accordance with an embodiment of thepresent invention.

[0034]FIG. 13 contains an image of an alternative switch elementmounting structure used in accordance with the invention.

[0035]FIG. 14 contains an image of switch clips used in one embodimentof the mounting structure of FIG. 13, in accordance with an embodimentof the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0036] The present invention is directed to an improved optical switchdevice with a rolling thin membrane or shutter which closes and opensupon application and removal of an electric field. For example, thepresent application provides improvements over devices of the typedescribed in U.S. Pat. No. 5,233,459 (the '459 patent hereinafter). Thatpatent is incorporated herein in its entirety by reference. Throughoutthe following detailed description, elements of the device or methodsused in fabricating the device of the invention are of the typedescribed in the '459 patent, unless what is being described isdifferent than or an improvement over an element, device or method offabrication described in the '459 patent.

[0037]FIG. 1A contains a top view image of a single MEMS rollingmembrane optical switch element 10 in accordance with one embodiment ofthe present invention, with the membrane in the closed or uncoiledstate, and FIG. 1B contains a schematic perspective view of the switchelement 10 with the membrane in the open or coiled state. The switchelement 10 includes a rolling membrane or shutter or shade 12 which isattached at its attachment end 16 to a substrate 14. The membrane 12includes corrugations 18 to aid in the coiling and uncoiling of themembrane 12. A membrane contact pad 24 is formed on the surface of thedevice 10 in electrical contact with the membrane. A substrate electrode25 is formed in contact with the substrate 14. When the operatingvoltage is applied across the two electrodes 24 and 25, the membrane 12uncoils over the substrate 14 into the configuration illustrated inFIG. 1. When the operating voltage is removed, the membrane 12 coils upaway from the substrate 14 back to the position of FIG. 1B.

[0038] A double-sided reflective surface or mirror 22 is formed in themembrane 12 near its center such that reflective surfaces are exposed onboth the top and bottom sides of the membrane. The mirror 22 issurrounded by circular corrugations 20 formed in the membrane to allowthe mirror 22 to be easily coiled and uncoiled and to allow the mirror22 to lay flat over the optical port in the substrate 12 when themembrane 12 is uncoiled onto the substrate 14.

[0039] In the invention described herein, the improvements made overprior devices, such as those described in the '459 patent, includerendering the substrate 14 highly transmissive and the movable membrane12 highly reflective. As a result, when the membrane is open, i.e.,coiled up, a light beam will pass through the substrate substantiallyunattenuated and unaberrated. When the shutter is closed, the light isreflected by the mirror.

[0040]FIG. 2A is a top plan view of one embodiment of the rolling mirroroptical switch element 10 of the invention. FIG. 2B is a schematiccross-sectional view of the rolling mirror optical switch element 10 ofthe invention taken along line A-A of FIG. 2A. FIG. 2C is a schematiccross-sectional view of the rolling mirror optical switch element 10 ofthe invention taken along line B-B of FIG. 2A. As shown in FIGS. 2A-2C,the membrane 12 opens and closes over an optical port portion 19 of thesubstrate 14. The substrate 14 can be made of a semiconductor materialsuch as silicon and it has formed on its surface an insulating layer 15.The membrane 12 is attached to the top of the insulating layer 15.

[0041] In the embodiment of FIGS. 2A-2C, the switch element 10 isfabricated on a silicon wafer. A hole 17 is etched through the back ofthe substrate 14 so that light passes through the device substantiallyunobstructed. When the shutter 12 is closed, i.e., rolled out, thereflective portion 22 spans the aperture 17 and reflects the light. FIG.3 contains an image of a rolling membrane optical switch device with themembrane in the open or coiled state, in accordance with one embodimentof the present invention. In this embodiment, the reflective portion inthe middle of the membrane is formed to have tensile stress which willtend to apply stretching to the mirror to keep the mirror flat. Themirror section of the membrane is designed to be under tensile stress sothat it is stretched flat like a drumhead. The mirror part of theshutter is also thinner and more flexible than the other areas of theshutter so that the forces stretching out the drumhead are small enoughto not easily distort the shutter. Also, the circular corrugations 20outside the mirror area 22 further relieve the forces on the rest of theshutter membrane.

[0042] In another embodiment, the substrate is made thin such that it issubstantially transparent at the wavelength of interest. Such a waferprovides substantially unobstructed transmission when the shutter 12 isopen and provides support for the shutter when it is closed. In thisembodiment, the wafer can be composed of an optically transparent butelectrically semiconducting material such that the actuation oroperating voltage is applied through or partially through the wafer.

[0043]FIG. 4A is a top plan view of another embodiment of the rollingmirror optical switch element 110 of the invention with the membrane inthe closed or uncoiled position.

[0044]FIG. 4B is a schematic cross-sectional view of the rolling mirroroptical switch element 110 of the invention taken along line A-A of FIG.4A. FIG. 4C is a schematic cross-sectional view of the rolling mirroroptical switch element 110 of the invention taken along line B-B of FIG.4A.

[0045] In this embodiment and the other embodiments described herein,the shutter can be less than 1 micron thick and can be up to 1,000microns across. The mirror can be approximately 400 microns across. Themirror 22 preferably comprises a reflective metal such as gold, aluminumor a gold/aluminum bilayer. Alternatively, thin film dielectric mirrorcoatings can be used. The stiffness in the membrane and mirror is low;the membrane and mirror are not rigid enough in general to assure a flatreflective surface. The flatness typically required in settings in whichthe device of the invention is applicable, such as fiber optic lasercommunications applications, is about 1000 Angstroms or less. In fact,it is this lack of rigidity which allows the mirror to be rolled andunrolled. The substrate, which is made of silicon, can have a flatenough surface. When the shutter lies in intimate contact with thesubstrate, the shutter will also be flat enough. In one embodiment, themirror is flat to within 1,000 Angstroms. In one embodiment, thesubstrate is thinned in the region of the mirror to the point where itbecomes transparent to the wavelength, e.g., infrared, of interest,allowing the substrate to provide support for the mirror when themembrane is unrolled and to act as a window for the transmitted beamwhen the membrane is rolled. An antireflection coating is used if thesubstrate is used as a window.

[0046] As noted above, in another embodiment, the substrate includes atapered hole or aperture 117 in the substrate under the membrane. Thehole cannot provide support for the mirror to keep it flat. The mirroris made flat by pulling it taut over the raised annular rim structure113 formed on the surface of the insulating layer 15 around the openingof the aperture 117.

[0047] In some cased it is desirable to use materials in the shuttermembrane that have a different coefficient of expansion than thesubstrate and sometimes the fabrication process requires that there is anet strain in the membrane relative to the substrate. This strain cancause buckling or distortion in the membrane, which can have a markedeffect on the actuation of the shutter and could reduce the mirrorflatness. To overcome these problems, the present invention provides animproved membrane.

[0048]FIG. 5A contains a schematic top view of a rolling membrane for anoptical switch device with strain relief slits 215 formed in theflexible membrane, in accordance with one embodiment of the presentinvention. The strain relief slits 215 are provided in the membrane 212as shown along the attachment edge of the membrane near attachment pads219.

[0049]FIG. 5B contains a schematic top view of a rolling membrane 312for an optical switch device with gas venting and strain relief slits315 formed in the flexible membrane, in accordance with one embodimentof the present invention. In addition to the strain relief benefit,these slits 315 also provide openings for the gas in the area of thedevice to move through the slits when the shutter is actuated. Since theshutter rolls out in a millisecond or less, the atmosphere around theshutter is pushed by the shutter, resisting its motion. Without theslits 315, this resistance is large enough to cause the shutter to bendduring actuation, since the resistance force is larger in the centerthan the edge. The slits 315 relieve the gas pressure and help make theforce more uniform, which improves the dynamic stability.

[0050]FIG. 5C contains a schematic view of a rolling membrane 412 for anoptical switch device with a tapered membrane 412 and a shortenedmembrane attachment edge 415, in accordance with one embodiment of thepresent invention. The side edges include tapered sections 417 such thatthe attachment edge 415 at the attachment pad 419 is shorter than themaximum width of the membrane 412.

[0051] An additional improvement provided in accordance with theinvention is reduced sticking between the shutter membrane and thesubstrate. Sticking is an important issue because it can cause acatastrophic failure of the shutter device. One of the causes forsticking is the high electric field between the shutter membrane and thepull down electrode in the substrate. Fields on the order of one millionvolts per centimeter are common for these shutter devices. Electricbreakdown and charge migration are expected to occur at these fieldstrengths and can cause sticking. In accordance with the invention, themembrane is modified to reduce the probability of sticking. FIGS. 6A-6Ccontain schematic views of a rolling membrane optical switch device 610with dimples formed in the membrane 612, in accordance with oneembodiment of the present invention. FIG. 6A is a top plan view of thisembodiment of the rolling mirror optical switch element 610 of theinvention with the membrane 612 in the closed or uncoiled position. FIG.6B is a schematic cross-sectional view of the rolling mirror opticalswitch element 610 of the invention taken along line A-A of FIG. 6A.FIG. 6C is a schematic cross-sectional view of the rolling mirroroptical switch element 610 of the invention taken along line B-B of FIG.6A.

[0052] In the embodiment of FIGS. 6A-6C, the membrane 612 includes anarray of dimples 613. In contrast with prior structures in which boththe substrate pull-down electrode and the membrane electrode arecontinuous sheets of metal, in this configuration of the invention, thedimples are fabricated with holes in one or both of the electrodes inthe area of and immediately surrounding the dimples 613. This removal ofelectrode material has the effect of greatly reducing the field in thearea of the dimple, which, in turn, greatly reduces the probability ofsticking.

[0053] FIGS. 7A-7B contain detailed schematic cross-sectional views ofalternate embodiments of the dimples 613 formed on the rolling membrane612 of the optical switch device of FIGS. 6A-6C. As shown in FIGS. 7A,the device 610 is formed on a substrate 615. A metal layer 617 is formedon the substrate 615, and a silicon dioxide layer 619 is formed on themetal layer 617 to a thickness of about 1,000 angstroms. A 3,000angstrom gap is left between the lower body of the device 610 and themembrane 610. The membrane is made from three layers of material,including a 1,000 angstrom thick silicon dioxide layer 623, a 1,000angstrom thick aluminum layer 625 and another 1,000 angstrom thicksilicon dioxide layer 627. The membrane 612 in the area of the dimple613 is shaped to create the dimple 613 to a width of about 3 microns.The dimple of FIG. 7B includes the same types of layers as that of FIG.7A. That is, the structure of FIG. 7B also includes a substrate 655, ametal layer 657, a 1,000 angstrom silicon dioxide layer 659, a 3,000angstrom gap 661, and a three-layer membrane 612, which includes two1,000 angstrom silicon dioxide layers 663 and 667 with a 1,000 angstromaluminum layer between them.

[0054] The difference between the structures of FIGS. 7A and 7B is inthe shapes of the layers. For example, in the device of FIG. 7A, thealuminum layer 625 is interrupted in the area of the dimple. Also, inFIG. 7B, in the area of the dimple, the metal layer 657 is interrupted.

[0055] In accordance with the invention, another approach to preventingsticking between the membrane and the substrate includes the addition ofa secondary, latching electrode, as shown in FIGS. 8A-8C, which containschematic views of a rolling membrane optical switch device 710 with alatch electrode 712, in accordance with one embodiment of the presentinvention. FIG. 8A is a top plan view of this embodiment of the rollingmirror optical switch element 670 of the invention with the membrane 712in the closed or uncoiled position. FIG. 8B is a schematiccross-sectional view of the rolling mirror optical switch element 710 ofthe invention taken along line A-A of FIG. 8A. FIG. 8C is a schematiccross-sectional view of the rolling mirror optical switch element 710 ofthe invention taken along line B-B of FIG. 8A.

[0056] The latch electrode 713 provides several functions. First, theextra electrode 713 provides an electric field within an air gap betweenthe end of the membrane and the substrate at the far end of the rolledout membrane 712 to hold down the shutter 712 once rollout has beenaccomplished. The intensity of the electric field is selected such thatthe end of the membrane is not pulled down into contact with thesubstrate, as shown in FIG. 8B. With this field in place, the rollout oroperating voltage in regions where the membrane is in contact with thesubstrate, which must be under the body of the membrane 712 to beeffective, can be turned off. Thus, except for the brief initial pulseto initiate and roll out the membrane 712, the field is eliminated inthe region of contact between the membrane 712 and the substrate,thereby reducing the potential for sticking. In one embodiment, the partof the membrane 712 over the latch electrode is physically held off thesubstrate surface by added support structures.

[0057] A second feature of this latching capability of the invention isa simplified drive circuit for use with the latching electrode. Becausethe latching electrode is separately accessible, the drive signals caneach be simple, binary-switched signals rather than high-to-low ramps. Athird feature of the latching electrode switch invention is the use ofrow/column address lines instead of individual address lines. That is,in a switch array such as the type described below, the (M,N)th switchcan be activated by energizing the Mth row of membrane electrodes andthe Nth column of pull-down electrodes and latching electrodes. Once the(M,N)th switch is latched, the power can then be removed from thepull-down electrode, and the latching voltage can be applied to the Mthrow of membrane electrodes and the Nth row of latching electrodes.

[0058] In another aspect, the invention is directed to an N×M opticalswitch array for use in optical data and telecommunicationsapplications. FIG. 9A contains a schematic perspective view of anoptical switch array 800, in accordance with an embodiment of thepresent invention, and FIG. 9B contains a detailed close-up schematicperspective view of a portion of the optical switch array 800 of FIG.9A. The array 800 incorporates N times M copies of any version of theimproved optical switch device 10 described herein fabricated using MEMStechnology. The improvements in the device allow it to alternatelyreflect and transmit a free-space-propagating optical data signal. Asshown in FIGS. 9A and 9B, the switch devices 10 are arranged on anN-by-M grid so that any of the M input signals can be routed arbitrarilyto the N output ports by activating, i.e., making reflective, the devicelocated at the (N,M)th grid location. The invention is also enabled bythe use of special high quality microlenses 803 and a unique mountingapproach for the various components.

[0059] As shown in FIGS. 9A and 9B, the array 800 selectively switcheslight between two orthogonal optical fiber arrays 805A and 805B. Lightfrom each optical fiber 805 is collimated by a microlens 803 before itis launched into the N×M grid of switches 10. In this embodiment, eachswitch is one of the improved optical switch devices described herein.As described above, each switch element contains the thin membrane 12that, because of internal stresses built in during fabrication, arenormally curled up into a roll or coil. When the switch is rolled up,the collimated light from the fiber is allowed to pass through the holeat the switch grid location. By selectively applying a voltage betweenthe membrane and the substrate of a selected switch, the respectivemembrane is uncurled or rolled out, revealing the reflective spot ormirror that will reflect the beam of light to the output port of thearray 800. The reflective mirror is designed to have a surface that iscurved when rolled up and flat when rolled out. The output ports of thearray 800 are identical to the input ports. A controller 810 isinterfaced to the array 800 for controlling the opening and closing ofswitches 10 at selected locations by selectively applying and removingthe operating and/or latching voltage as described above to theappropriate rows and columns of the array 800.

[0060] As shown in FIGS. 9A and 9B, the switches 10 are arranged in agrid configuration and are supported on a microbench 807. The fibers 805and microlenses 803 are supported by supports 509.

[0061]FIG. 10 contains an image of the optical switch array 800 heinvention illustrating multiple optical switch elements 10 the open andclosed states.

[0062]FIG. 11 contains a schematic perspective view of an optical switcharray 900, prior to installation of all of the switch elements 10. Itillustrates features of the approach to assembling the switch array 900in accordance with an embodiment of the invention, as well as beampropagation through the matrix. As described in detail above, the switchelements 10 are fabricated lying down in the plane of the silicon wafersubstrate and may be diced into linear arrays of any length, from one upto the number that fits across the width of the wafer. The individualdie or linked linear arrays 910 are mounted on an optical microbench 907“tombstone” style at the intersection of the path of a beam of lightfrom one fiber 805 to another, as shown with only partial population inFIG. 11 for clarity and ease of illustration.

[0063] The switches can be attached to the bench 907 in any of severalways. First, the switches can be mounted using purely passive alignment.Using this approach, the individual die or the linked dice are mounteddirectly into matching mounting structures machined into the opticalbench 907. FIG. 12 contains an image of an example of such a mountingstructure 919. The structure 919 includes a row of integral spring clips921, each for holding one die.

[0064] Another mounting approach is shown in FIG. 13, which illustratesmounting and alignment structures (MAMS) described in a U.S. provisionalpatent application entitled, “Mounting and Alignment Structures forOptical Communications Components,” Ser. No. 60/186,925, filed on Mar.3, 2000 and a U.S. non-provisional patent application entitled,“Mounting and Alignment Structures for Optical Components,” Ser. No.09/648,348, filed on Aug. 25, 2000. Those applications are incorporatedherein in their entirety by reference. Under this approach, the switchesare placed on the MAMS by standard pack-and-place technology, as used inthe semiconductor industry, and affixed using solder. The switch-bearingMAMS are similarly placed and affixed to the bench at the opticalintersections between the input and output fiber ports. Only after theMAMS are soldered in place on the optical bench are they aligned usingactive alignment algorithms. A variation on this approach occurs whenthe MAMS are built in linear arrays. In this case, the individualswitches are mounted on linear MAMS arrays of appropriate lengths, andthen the array is mounted on the bench. Again, final alignment of eachswitch takes place using active alignment after mounting to the bench iscomplete.

[0065] A hybrid mounting approach is based on a spring clip MAMS, asshown in FIG. 14. For this approach, two spring clip MAMS are used toform the interface between the die/array and the microbench. Unlike thefirst approach, these MAMS are mounted and aligned passively, and thenthe switch dice are inserted. The electrical connections to the switchclips are made through traces on the optical bench. If the spring clipmount of FIG. 14 is used, then each spring arm carries the signal fromthe bench to the switch electrodes.

[0066] The interface between the optical fibers and the switch module isanother important feature of the invention, since it allows the entirepackage to be made small, robust, and inexpensive. Referring again toFIG. 11, in one embodiment, an array of fiber collimators 911, arrangedin a 90-degree comer with a second array of collimators, are used totransform light from similarly arranged rows of optical fiber to arraysof parallel beams of collimated light. These beams are deflected by theswitches to the second lens array, which focuses the beams into theoutput fibers. This interface is created using linear arrays of MAMS tohold and align both the fibers and the collimating lenses. Thecollimating lenses are preferably manufactured by a patented masstransport process of the type described in U.S. Pat. No. 5,807,622,which is incorporated herein in its entirety by reference. However,other microlens fabrication techniques, such as binary optics or castmicro-refractive lenses, could also be used.

[0067] These lens and fiber arrays can be constructed from individualMAMS or from linearly connected arrays of MAMS. A feature of a MAMS isthat it can be critically aligned using active feedback after it hasbeen installed on the bench and after the lens or fiber has beeninstalled on it.

[0068] While this invention has been particularly shown and describedwith references to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the following claims.

1. An optical switch array comprising: a plurality of optical switchelements disposed in a plurality of rows and columns, each opticalswitch element comprising: a substrate, and a flexible membrane attachedat at least one end to a surface of the substrate in proximity to anoptical port portion of the substrate, the flexible membrane beingconfigured such that, in a first state, the flexible membrane isdisposed over the optical port portion of the substrate such that lightdirected toward the optical port portion of the substrate impinges onthe flexible membrane, and, in a second state, the flexible membrane isdisposed to expose the optical port portion of the substrate such thatlight directed toward the optical port portion of the substrate impingeson the optical port portion of the substrate; and a controller coupledto the plurality of optical switch elements for selectively applying anoperating voltage across substrates and flexible membranes of selectedswitch elements to operate the optical switch array.
 2. The opticalswitch array of claim 1 , wherein each flexible membrane is formed suchthat in the second state, the flexible membrane is coiled away from theoptical port portion of its respective substrate, and, in the firststate, the flexible membrane is uncoiled over its respective opticalport portion of the substrate.
 3. The optical switch array of claim 2 ,wherein each flexible membrane is normally in a coiled condition, and,upon application of the operating voltage across the flexible membraneand its respective substrate, the flexible membrane uncoils over itsrespective optical port portion of the substrate.
 4. The optical switcharray of claim 1 , wherein the substrate of each optical switch elementis a portion of a single substrate of the optical switch array.
 5. Theoptical switch array of claim 1 , wherein each optical element comprisesan aperture formed through the optical port portion of its substratesuch that, when its respective flexible membrane is in the first state,the flexible membrane is disposed over the aperture, and, when theflexible membrane is in the second state, light directed toward theoptical port portion of the substrate passes through the aperture. 6.The optical switch array of claim 1 , further comprising an array ofoptical fibers which emits optical signals into the switch array.
 7. Theoptical switch array of claim 6 , further comprising a second array ofoptical fibers which collects the optical signals after they arereflected by the switch array.
 8. An optical switching methodcomprising: providing a plurality of optical switch elements disposed ina plurality of rows and columns, each optical switch element comprising:a substrate, and a flexible membrane attached at at least one end to asurface of the substrate in proximity to an optical port portion of thesubstrate, the flexible membrane being configured such that, in a firststate, the flexible membrane is disposed over the optical port portionof the substrate such that light directed toward the optical portportion of the substrate impinges on the flexible membrane, and, in asecond state, the flexible membrane is disposed to expose the opticalport portion of the substrate such that light directed toward theoptical port portion of the substrate impinges on the optical portportion of the substrate; coupling a controller to the plurality ofoptical switch elements; and selectively applying an operating voltageacross substrates and flexible membranes of selected switch elements tooperate the optical switch array.
 9. The optical switching method ofclaim 8 , further comprising forming each flexible membrane such that inthe second state, the flexible membrane is coiled away from the opticalport portion of its respective substrate, and, in the first state, theflexible membrane is uncoiled over its respective optical port portionof the substrate.
 10. The optical switching method of claim 9 , furthercomprising forming each optical switch element such that each flexiblemembrane is normally in a coiled condition, and, upon application of theoperating voltage across the flexible membrane and its respectivesubstrate, the flexible membrane uncoils over its respective opticalport portion of the substrate.
 11. The optical switching method of claim8 , wherein the substrate of each optical switch element is a portion ofa single substrate of the optical switch array.
 12. The opticalswitching method of claim 8 , further comprising forming each opticalswitch element with an aperture through the optical port portion of itssubstrate such that, when its respective flexible membrane is in thefirst state, the flexible membrane is disposed over the aperture, and,when the flexible membrane is in the second state, light directed towardthe optical port portion of the substrate passes through the aperture.13. The optical switching method of claim 8 , further comprisingproviding an array of optical fibers which emits optical signals intothe switch array.
 14. The optical switching method of claim 13 , furthercomprising providing a second array of optical fibers which collects theoptical signals after they are reflected by the switch array.
 15. Anoptical switch system comprising: an optical bench; an array of beamswitches installed tombstone fashion on the optical bench, the beamswitches comprising membranes, which in a first state reflect lightbeams and in a second state enable transmission of the light beamsthrough the beam switches; at least one input optical fiber forlaunching a light beam into the array of beam switches; and at least oneoutput optical fiber for receiving the light beam after transmissionthrough the array of beam switches.
 16. An optical switch system asclaimed in claim 15 , further comprising an array of input opticalfibers for launching multiple light beams into the array of beamswitches.
 17. An optical switch system as claimed in claim 16 , furthercomprising an array of collimator lens between endfaces of the opticalfibers of the input optical fiber array and the array of beam switchesfor improving collimation of the light beams during propagation throughthe array of beam switches.
 18. An optical switch system as claimed inclaim 15 , further comprising an array of output optical fibers forreceiving multiple light beams after transmission through the array ofbeam switches.
 19. An optical switch system as claimed in claim 18 ,further comprising an array of focusing lenses for coupling the multiplelight beams into the output optical fiber array after propagationthrough the array of beam switches.
 20. An optical switch system asclaimed in claim 15 , wherein the array beam switches are aligned inrows.
 21. An optical switch system as claimed in claim 20 , wherein therows extend in a direction that is angled relative to an axis of theinput optical fiber and the output optical fiber.
 22. An optical switchsystem as claimed in claim 20 , wherein the rows extend in a directionsuch that when the beam switches are in the first state, light isreflected form the input optical fiber to the output optical fiber. 23.An optical switch system as claimed in claim 15 , wherein the array ofbeam switches are arranged in a two dimensional grid.